Extreme ultraviolet lithography (“EUVL”) is one of the leading technology options to replace optical lithography for volume semiconductor manufacturing at feature sizes <20 nm. The extremely short wavelength (13.4 nm) is a key enabling factor for high resolution required at multiple technology generations. In addition, the overall system concept—scanning exposure, projection optics, mask format, and resist technology—is quite similar to that used for current optical technologies. Like previous lithography generations, EUVL consists of resist technology, exposure tool technology, and mask technology. The key challenges are EUV source power and throughput. Any improvement in EUV power source will directly impact the currently strict resist sensitivity specification. Indeed, a major issue in EUVL imaging is resist sensitivity, the lower the sensitivity, the greater the source power that is needed or the longer the exposure time that is required to fully expose the resist. The lower the power levels, the more noise affects the line edge roughness (“LER”) of the printed lines.
Improving extreme ultraviolet (“EUV”) sensitivity is a key enabling factor. It has been shown that EUV light absorption cross-section and secondary electron generation yield are critical factors for EUV sensitivity. One way to increase EUV photoresist sensitivity is by increasing its absorption cross-section at 13.5 nm, which is an atomic property of the material that can be theoretically calculated using known atomic absorptions. Typical atoms that make up resist materials, such as carbon, oxygen, hydrogen, and nitrogen possess very weak absorption at 13.5 nm. A fluorine atom has slightly higher absorption and has been used in the search for high EUV absorbing photoresist.
Iodine has remarkably high absorption cross-section at EUV radiation. Recent patent application JP 2015-161823 discloses iodine-containing monomers and corresponding polymers useful for lithographic processing. However none of these monomers contemplated an extended chain to improve the incorporation of iodine-containing monomers. There is still a need for iodine-rich monomers and corresponding polymers that possess good solubility and that imparts improved sensitivity under EUV exposure.